Great circle ruling device



R. PFLUGER GREAT CIRCLE RULING DEVICE Filed March 24, 1930 March 15, 1932.

Patented Mar. 15, 1932 I I 1 849 202 UNITED STATES PATENT OFFICE BUDOLF PFLUGER, HAMBURG, GERMANY GREAT CIRCLE RULING DEVICE Application filed March 24, 1930, Serial No. 438,511, and in Germany Hatch. 8, 1928.

The invention relatesto an instrument for Figure 2 is a section on the line 2-2 of drawing with mathematical accuracy great F lgure 1.

circles and parallel circles on spherical draw- Figure 3 is a section on the line 3-3 of ing surfaces. The instrument is suitable for Figure 1. 5 checking all calculations in spherical trigo- Flgure 4: is an enlarged detail section of 55 nometry and its applications.\ Particularly the joint between the rulers of the invention. does it enable the graphic determination of In the embodiment of the invention here the position of a ship to be made for navigashown there is illustrated a sphere 1O suption purposes. Further the instrument is ported conventionally on a stand 11. A

particularly suitable for demonstration purgroove 12 is formed in the sphere at the o0 poses in mathematical instruction. equator thereof and in this groove is slidably Spherical and hemi-spherical drawing surfitted a great circle bar 13 in the form of a faces are already well known, but means have ring or annulus. Opposite diametrically disbeen lacking to enable the great and parallel posed pivots 14 on this bar 13 support a sub- 5 circles, necessary for mathematical calculastantially semi-circular bar 15 forming the 86 tions, to be drawn with the essential accuracy. are of a great circle. 1 For this purpose it has already been pro- By means of the movement of the ring 13 posed, it is true, to use a device consisting of the pivot points 1d may-be shifted to any demutually rotatable bands of three quarters sired positions around the equator of the the circumefence of the circle, this device besphere and the bar 15 may be adjusted to any 70.

ing clamped to the spherical surface. The desired angle relative to the bar 13. Thus a mathematically great circles necessary for w de range of problems relative to spherical measuring purposes may however not be trigonometry may be charted on the sphere. drawn by this method as the fixing of the What is claimed, is: i

hoop to the sphere is not without imperfec- 1. The combination wlth a sphere having a tion. In such an instrument, when the bands great circle groove extending therearound, of form an acute angle to each other, the spheria bar forming a great circle mounted on said cal curvature decreasing only slowly along sphere and engagm the groove to slide therethe bearing surfaces of the rule (only at 18 in, and a substantia ly semi-circular bar havlateral to the great circle is there a decrease ing its'ends pivoted to diametrically oppoof 5%) offers no degree of certainty of an site points of the first bar. efi'ective great circle being drawn, owing to 2. The combinationwith a sphere having the inevitable springing and lateral bending. an equatorial groove, of a circular bar form The fixing of a plane must be done positiveing the equatorial circle of said sphere and 35 ly and this can be done with mathematical having sliding engagement with the groove, accuracy only through three points. If a and a great circle arc bar having its ends pivplane so fixed gives as a section with a sphere oted to diametrically opposite points of the a great circle also, the plane must moreover circular bar. onilzgiiln the centre point of the sphere as a In testimony whereof I aliix my signature.

so on point.

With the instrument forming the subject RUDOLF PFLUGER of the invention, it is possible to draw the great circle with such mathematical accuracy, as is technically possible.

45 The essence of the invention will now be v explained in conjunction with the accompanying drawings. a

Figure 1 is a side elevation of the invention with the sphere shown on a conventional 50 mounting. 

